Mesoporous silica nanostructures (MSNs) attract high interest due to their unique and tunable physical chemical features, including high specific surface area and large pore volume, that hold a great potential in a variety of fields, i.e., adsorption, catalysis, and biomedicine. An essential feature for biomedical application of MSNs is limiting MSN size in the sub-micrometer regime to control uptake and cell viability. However, careful size tuning in such a regime remains still challenging. We aim to tackling this issue by developing two synthetic procedures for MSN size modulation, performed in homogenous aqueous/ethanol solution or two-phase aqueous/ethyl acetate system. Both approaches make use of tetraethyl orthosilicate as precursor, in the presence of cetyltrimethylammonium bromide, as structure-directing agent, and NaOH, as base-catalyst. NaOH catalyzed syntheses usually require high temperature (>80 °C) and large reaction medium volume to trigger MSN formation and limit aggregation. Here, a successful modulation of MSNs size from 40 up to 150 nm is demonstrated to be achieved by purposely balancing synthesis conditions, being able, in addition, to keep reaction temperature not higher than 50 °C (30 °C and 50 °C, respectively) and reaction mixture volume low. Through a comprehensive and in-depth systematic morphological and structural investigation, the mechanism and kinetics that sustain the control of MSNs size in such low dimensional regime are defined, highlighting that modulation of size and pores of the structures are mainly mediated by base concentration, reaction time and temperature and ageing, for the homogenous phase approach, and by temperature for the two-phase synthesis. Finally, an in vitro study is performed on bEnd.3 cells to investigate on the cytotoxicity of the MNSs.

Shedding light on the interaction between inorganic nanoparticles (NPs) and living microorganisms is at the basis of the development of biohybrid technologies with improved performance. Au NPs have been shown to be able to improve the extracellular electron transfer (EET) in intact bacterial cells interfaced with an electrode; however, detailed information on the role of NP-surface properties in their interaction with bacterial membranes is still lacking. Herein, we unveil how the surface functionalization of Au NPs influences their interaction with photosynthetic bacteria, focusing on cell morphology, growth kinetics, NPs localization, and electrocatalytic performance. We show that functionalization of Au NPs with cysteine in the zwitterionic form results in a uniform NPs distribution in purple bacteria, specifically locating the NPs within the outer-membrane/periplasmic space of bacterial cells. These biohybrid cells, when coupled with an electrode, exhibit enhanced EET and increased (photo)current generation, paving the way for the future development of rationally designed biohybrid electrochemical systems.